Tools for use downhole in the completion of a wellbore are generally well known. For example, perforation devices are commonly deployed downhole on wireline, cable, or on tubing string, and sealing devices such as bridge plugs and straddle packers are commonly used to isolate portions of the wellbore during fluid treatment. As such, tools are exposed to varying conditions during use, and improvements have evolved over time to address problems typically encountered downhole.
The Applicants have previously described a tool and method for use in the perforation and treatment of multiple wellbore intervals. That tool included a jet perforation device and sealing assembly, with an equalization valve for controlling fluid flow through and about the assembly. Fluid treatment is applied down the wellbore annulus to treat the uppermost perforated zone.
When multiple pre-existing perforations are to be treated, application of the treatment fluid down the wellbore annulus is not desirable, as perforations cannot be treated selectively by this method. Typically, an isolation device is required. Cup seals are known for use in straddle tools and other isolation tools, but are not well suited for applications requiring repeated use in a single run downhole due to the risk of wear and failure should the tool assembly slide within the wellbore while the seals are set. This risk is greater in applications where sand or other debris is present downhole, as the cup seals may fail to fully seal against the casing in the presence of sand or other solids, leading to sliding of the seals and premature wear.
Use of any sealing device in the presence of significant amounts of sand or other solids increases the risk of tool malfunction. Further, the tool may become stuck downhole should a solids blockage occur during treatment, or when the formation expels solids upon release of hydraulic pressure in the wellbore annulus when treatment is complete. Typical completion assemblies have many moving components to provide actuation for various downhole functions, and the presence of sand or other solids within these actuation mechanisms would risk jamming these mechanisms, potentially causing a malfunction or permanent damage to the tool or well. Correcting such a situation is costly, and poses significant delays in the completion of the well. Accordingly, well operators, fracturing companies, and tool suppliers/service providers are typically very cautious in their selection of fluids and tools for use in completion operations.